Barking method



April 10, 1956 R. R. ALEXANDER BARKING METHOD Filed June 1 195G 7Z7Z/4/exa-nder v/ lll/IIllf 4w IIIl/rllllflfllllfll! If!!! IN VE N T0}? flTTORNEY United States harem:

EARRING Martino Ronald Rouleau Alexander, Carthage, N. 51., assignor to Carthage Machine Company, Carthage, N. 1., a corporation of New York Application June 1, 1950, Serial No. 165,469

7 Claims. (Cl. 144-609) This invention relates to a process and apparatus for efiiciently and economically separating bark from wood material, such as logs, bolts, saw mill waste, wood chips and the like, without damage to the fibre structure of the wood and without loss of wood.

Processes and apparatus for separating the bark from logs, bolts, slabs and the like have been the subject of exhaustive investigation for many years. Various processes and apparatus have been devised and are well known and widely used. In general, the known processes and apparatus involve the employment of mechanical and hydraulic devices such as, for example, bark peeling machines, bark crushing machi es, barking drums in which a drum loaded with logs is rotated and the bark is removed by the action of the logs acting one against the other in the presencecf water, or hydraulic devices in which jets of water under very high pressure are employed to separate the bark, and combinations of various known processes and apparatus designed to serve specific purposes. A recapitulaticn of bark-peeling machines and methods is found in publication No. D1730 of the United States Department of Agriculture, Forest Service, Forest Products Laboratory, entitled Bark Peeling Methods and Apparatus, dated January 1949. 7

There is what is known as the cambium layer between the bark and the wood. This relatively thin layer of cambium cells constitutes the line of adhesion of the bark to the wood. The cambium cells while fragile and easily broken in fresh, spring-cut wood, become relatively tough and hard to break in the dormant season. Bark peeling processes and apparatus are devised, generally, to separate the bark from the Wood at their natural point of cleavage, known technically as the cambium layer.

It is known that the carnbium layer may be softened by water and its adhesive properties reduced accordingly and this knowledge is employed in processes in which the wood material is soaked in an aqueous solution for a period of time suflicient to soften the cambium layer after which the bark may be removed by mechanical means. This principle is also employed to a lesser extent in barking drums wherein the bark is removed principally by mechanical action aided by the softening action of water. These processes have the disadvantages that relatively costly equipment is involved, the treatment requires long time intervals, there is danger of damaging the wood fibres and they are restricted to the treatment of logs and are not adapted to remove the bark from small material such as slabs and edgings and other forms of saw mill Waste, branches, chips and the like, all of which are of potential commercial value in the manufacture of wood products and derivatives.

l have found that the bark may be quickly, effectively and economically separated from the wood material regardless of the size of the wood pieces by subjecting the wood pieces to a relatively high pressure, of the order of 100 pounds per square inch and above, in a pressure vessel. The pressure is maintained for a relatively short period of time and then suddenly sharply reduced to ll cc about atmospheric pressure. While the invention is independent of hypothetical considerations, it appears that the pressure functions to compress and/or crush the weaker carnbium cell layer between the two harder bark and wood layers. In general, the pressure medium tends to penetrate through the bark into the Cambium cell layer, but inner bark conditions have been noted in isolated in stances which did not permit the pressure intrusion. It is found that regardless of whether or not the pressure medium penetrates into the cambium layer, the result is the same. Upon the sudden release of the pressure, the bark is literally exploded from the wood, evidently by reflex action of the cambium cell layer.

This reflex action is materially aided by the infiltration of the high pressure medium, which penetrates the cambium cells through the pervious bark structure, and with the sudden release of the pressure the cambiurn cell layer, and its adhesive and cohesive properties, is destroyed by a bursting action. This action occurs in the bark structure also, the outer bark bursting into fine fragments and the inner bark bursting into wool-like material.

Normally, the pressure medium will be a fluid selected from the points of view of cost, availability, compressibility, and its eil'ect on the wood. For example, in debarking saw mill and pulp wood, a fluid would not be employed which would discolour the wood. I have found that a hot gas such as steam'rnay be employed with advantage in the pressure vessel as the pressure exerting medium. The application of heat to the wood in green or semi-dried condition results in the expansion of the gases within the cell structure and since the moisture content of the Cambium cells, new growth and bark cells is greater than that of the older growth and the cell structure of those cells is weaker than the cell structure of the older growth, they are afiected first. Further, when heat is applied, because of the difference of the bark and wood structures, there is unevenness in their expansion rate, direction and extent and they tend to separate easily at their point of cleavage which is the Cambium cell layer.

The sudden release of the pressure serves a further useful purpose in that the rush of hot gases from the pressure vessel serves to clear the bark from and scours the outer surface of the wood material. This is effected without damage to the wood fibres underlying the cambium cells.

I have found further that there is a definite relationship between the amount of heat and pressure applied and the time interval of the treatment. Specifically, l have found that the higher the pressure employed the shorter is the time interval necessary for the crushing and destroying action of the cambium cells. This is important in that the structure of the wood material may be adversely afiected by the intrusion of heat and pressure into its cell structure if it is subjected to the high pressure for too long a period. For example, fibres may become loosened from the surface of the wood, particularly at the ends, on the sudden release of the pressure. Therefore, the wood material must be subiected to the relatively high pressure for a time interval, wi hin reasonable limits of course, only suflicieut to compress and crush the cambium cell layer between the opposing bark and wood layers.

An understanding of the process and the manner in which it is operated may be had from the following description, reference being made to the accompanying drav ing in which:

Figure l is a front elevation in section of a pressure vessel and associated parts suitable for carrying out the process of the present invention; and

Figure 2 is a top plan view.

Like reference characters refer to like parts throughout the specification and drawing.

Referring to the drawing, the numeral it indicates a it is difiicult to predict the proper time interval.

' the process normally would be operated.

The pressure vessel is provided with a closed end 3.1 and an openend 11a closed by ahingedly mounted cover '12. The cover 12 is hingedly secured, as at 13, to one side of the vessel and its unattached side is formed with a tongue 1 which is engaged bythe free end of a pivotally 'mounted clamping member '15. The upper or free end of the clamping member 15 is bifurcated to form a yoked latch within which the tongue 14 is received in clamping engagement. A bolt 16 is threaded through the upper end of the latch to engage, in its tightened position, and bear against the tongue 14, 'thus to hold the cover member tightly and securely in place. V

A gasket 17 is inserted between the end of the cylinder and the opposing face of the cover member, to seal the joint between the opposing faces of the end ofthe cylinder and the cover member when the cover'is locked in place.

The cover member may be opened easily and quickly by loosening the bolt 16 and pivoting the latch out of its engagement with the tongue 14.

A compressible fluid such as steam or other heated or unheated gas is introduced into the cylinder through a pipe 18 which is extended through the rearward or closed end of the cylinder. This pipe 18 is connected at its inlet end to a source of'fluid under pressure, such as a steam boiler'3l A valve 19 is provided in the pipe is to regulate the fiow of fluid to the cylinder. An outlet conduit 29 for exhaust gas may be provided which extends from the cylinder. -A quick opening valve 21 is provided in this conduit. Alternatively, the clamping arm 15 may be provided with a trip arm 22 which may be employed as a lever to swing'the member 16 into and out of its engagement with the tongue 14.

The cylinder is charged with wood material such as logs, from which the bark is to be removed. The cover 12 is closed and locked tightly in place by the latch member 15. The valve 19 is opened, the valve 21 is closed and fluid under pressure is admitted to the cylinder until a pressure has been generated within the cylinder of the order of, for example, 100 pounds per square inch or more. This pressure is maintained for a period of time sufficient to compress and crush the cambium cell layer between the bark and the wood layers of the wood material being treated whereafter the valve 19' is closed and either the valve 21 is quickly opened to suddenly relieve the pressure or, alternative: the arm 22 is tripped to release the member 15 from its engagement with the tongue 14, thus to permit the cover to be blown open under the internal pressure of the'cylinder. in this latter instance, the contents of the cylinder are in effect blown with explosive force from the cylinder. The sudden release of the pressure servesto burst the bark from the wood material by reflex action of the cambium cell layer and the rush of 'hot gasesfrorn the cylinder serves 'to clean the outsidesurface of the wood material.

Depending upon the type and the condition of the wood being treated, I have found that pressures of from .ZOOpounds to 500 pounds per square inch maintained over periods of from about seconds to 2.5 seconds duration serves to remove completely thebark from the 7 square inch and lower and as high as 800 pounds perl square Inch and above. At the lower pressures, the time required'for thetreatment' is extended to the extent that As the tlme interval is extended, pressuretends to build upin inch, for exampleof the order of 800 pounds per square inch and above, but there is difiiculty in obtaining the very short time interval of the treatment without employing costly equipment. The process is operated, therefore, at pressures above 100 pounds per square inch and preferably below 800 pounds per square inch.

in the operation of the process, I have found that the condition of the wood, that is green, weathered, or dry, has very little efiect on the operation of the process. How

ever, there appearsto be definite species groups wherein the component'members react to thetreatment in alike 'manner for all practical purposes. In general, 'it'appears that coniferous species react more readily to the'treatment than do the deciduous species and thus require lower pressures and shorter time intervals of treatment than do the deciduous species.

The size and/or the age of the wood material appears to make little difierence in the operation as-similar results have been obtained from the similar treatment of sizes ranging from twigs and wood chips through large sizes,

such as pulp wood and saw log diameters.

Steam is the preferable pressure producing medium in 7 that it may be produced inexpensively and conveniently and in use it serves the functions 'of generating the reuired pressure conditions and, also, has a softening efiect on the cambium cells. However, other compressible fluids maybe employed with equally satisfactory results, for example, compressed air, hot gases, and gases containing solvents for the cambium cells.

Immediately following the separation of the bark from the wood material, the mixture of wood and bark may be discharged into a bath of cold water. The bark material, due to the separation treatment and the condition the wood structure to the extent that pressure brooming of the ends of the bolts was noted. The treatment can be conducted at pressures above 500 pounds per square in which it leaves the pressure vessel, rapidly absorbs water and sinks to the bottom of the bath whereas the solid Q wood material floats on the surface thereby making possible a quick and effective separation of the wood from the bark. Rotten wood and refuse appear to act in a manner similar to that of the bark. g

I have found the process of the present invention for debarking wood material to have a number of important advantages. The process is highly etlective to produce wood material free from bark and ready for subsequent operations, such as for sawing into lumber, and for chipping or r Y grinding for pulp and paper making. Also, it provides an inexpensive treatment for the separation of the bark and the recovery of clean wood from saw mill Waste such as slabs, and edgingsthereby making possible the employment of such waste'material in pulp and paper making operations and in the production of wood derivatives. It has the further important advantage in that the process may be employed for de-barking wood Without Waste and without damage to the wood structure regardless of the sizes and shapes of the wood to be treated.

What I claim as new and desire to protect Patent of the United States is:

l. The method of de-barking wood which comprises the steps of subjecting the wood in a pressure vessel to the action of a fluid at a pressure of at least about pounds by Letters per square inch for a period of time sufficient for the fluid to penetrate the bark and compress the cambium 'cell layers between the bark and the wood layers, and

of steam under a pressure of at least about 100 pounds per square inch for a period of time sulficient for the steam to penetrate the bark and compress the cambium cell layer between the bark and the wood layers, and thereafter suddenly reducing the pressure to about atmospheric pressure to elfect separation of the bark from the wood by reflex action of the cambium cell layer.

3. The method of de-barking wood which comprises the steps of subjecting the wood in a pressure vessel to the action of steam at a pressure of at least about 100 pounds per square inch for a period of time sufiicient for the fluid to penetrate the bark and compress the cambium cell layer between the bark and the wood layers but insufficient for the steam to penetrate the wood below the cambium layer, and thereafter suddenly releasing the pressure to reduce it to about atmospheric pressure, whereby the bark is separated from the wood by the reflex action of the cambium cell layer.

4. The method of de-barking wood which comprises the steps of subjecting the wood in a pressure vessel to the action of a fluid at a pressure within the range of from about 100 to about 800 pounds per square inch for a period of time sufiicient for the fluid to penetrate the bark and compress the cambium cell layer between the bark and the Wood layers and then suddenly reducing the pressure to about atmospheric pressure, whereby the bark is separated from the wood by reflex action of the cambium cell layer.

5 The method of de-barking wood material which com prises the steps of subjecting the wood in a pressure vessel to the action of steam under a pressure Within the range of from about 100 to about 800 pounds per square inch for a period of time suflicient for the steam to penetrate the bark and penetrate the cambium cell layer between the bark and wood layer but insufficient for the steam to penetrate the wood below the cambium layer, and thereafter suddenly reducing the pressure to about atmospheric pressure, whereby the bark is separated from the wood by reflex action of the cambium cell layer.

6. The method of de-barking wood which comprises the steps of subjecting the wood in a pressure vessel to the action of a fluid at a pressure of at least 100 pounds per square inch for a period of time suflicient for the fluid to penetrate the bark and compress the cambium cell layers between the bark and the wood layers, and thereafter suddenly reducing the pressure to about atmospheric pressure, whereby the bark is separated from the wood by reflex action of the cambium cell layer, and simultaneously discharging the Wood and the separated bark from the pressure vessel into a bath of water, and separately removing the floating wood and the submerged bark from the bath of water.

7. The method of de-barking wood material which comprises the steps of subjecting the wood in a pressure vessel to the action of steam under pressure within the range of from about 100 to about 800 pounds per square inch for a period of time sufi'icient for the steam to penetrate the bark and to compress the cambium cell layer between the bark and the wood layers, and thereafter suddenly reducing the pressure to about atmospheric pressure, whereby the bark is separated from the wood by reflex action of the cambium cell layer, and simultaneously discharging the wood and the separated bark from the pressure vessel into a bath of water, and separately removing the wood and the bark from the bath of water.

References Cited in the file of this patent UNITED STATES PATENTS 72,873 Maitre Dec. 31, 1867 1,281,155 Guettler Oct. 8, 1918 1,433,928 Baxter Oct. 31, 1922 1,448,520 Castruccio Mar. 13, 1923 

